Research project: Evolution of Carbon Cycle Dynamics (eCCD)

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The global carbon cycle comprises a set of reservoirs (ocean, atmosphere, biosphere, sediments) interconnected by fluxes. The storage of carbon in each reservoir and the individual fluxes can change with time. The eCCD project addresses a signature of this change over the last 150 million years, namely the changing composition of deep ocean sediments reflected in the “lysocline curve” that delineates the depth above/below which calcium carbonate dissolves.

Project Overview

The concentration of CO2 in the atmosphere has varied enormously over the last few hundred of millions of years. The chemistry of the oceans also slowly varies with time, and the organisms living within the ocean change and evolve. The details of how the carbon cycle 'works', and of particular importance, how well (or not) the concentration of CO2 in the atmosphere (and hence climate) is regulated, thus also changes on geological time-scales. This creates challenges, for instance, in understanding the causes and consequences of past global warming like events and how they can be related to the future. The sediments slowly accumulating in the deep ocean reflect everything that goes on around them and above them, both chemically and biologically. In particular, the mineral calcium carbonate (CaCO3), which can be found in the form of chalk and limestone rocks today, is a material commonly used in constructing shells and skeletons by marine organisms. Hence, the amount of CaCO3 being buried in sediments tells us something about ancient organisms and ecosystems. In addition, CaCO3 will start dissolving in seawater if the conditions are acidic or the depth (and thus pressure) is very intense, such as at the very bottom of the open ocean. How much of the CaCO3 originally created by organisms that remains and is not dissolved in sediments, thus also tells us something about past ocean chemistry, depth, and when data from many locations is available, ocean circulation.

In this project, by compiling the records from hundreds of different sediment cores recovered in the past decades, we will reconstruct change in depth and time, in the different ocean basins, of the key balance between surface ocean biological processes and deep ocean chemical and circulation processes. Because sediment records exist as far bask as the Mesozoic and well before the dinosaurs went extinct, we will start there. However, the interpretation of the “lysocline curve” we will produce is not straightforward, because multiple environmental changes can all push and pull this balance point in different directions and with different strengths. We will therefore also configure a computer model representation of the Earth's climate and oceans, its carbon cycle, ocean chemistry, and the composition of sediments in the deep sea for these times in the past. We will use this to explore how the different possible changes in the carbon cycle affect the balance point, and by comparing to our new curve through time, interpret how the carbon cycle has changed over the past 150 million years. This will also allow us to understand how the sensitivity of the carbon cycle and hence climate, changes in time after a perturbation, such as by massive greenhouse gas releases. Hence we will not only be able to answer the question: do we live in a particularly 'lucky' or 'unlucky' time in terms of how sensitive our global environment is to the burning of fossil fuels, but we will know why the Earth system responds with a certain degree of sensitivity.